"Our Curiosity measurements show that the current Martian atmosphere contains very little or no methane, a gas that on Earth is produced by biological processes, and is therefore a potential signature of life on Mars," Webster said.

Over the past decade, researchers have reported "plumes" of the gas in the Martian atmosphere, sparking interest in the possibility of a biological source on Mars. However, since those reports were made from either Earth or an orbiting satellite, such claims have remained controversial.

The researchers reported in the journal Science that they ruled out the possibility of methane disappearing quickly from the Martian atmosphere.

"Methane is persistent. It would last for hundreds of years in the Martian atmosphere," said one of the paper's co-authors Sushil Atreya of the University of Michigan.

"Without a way to take it out of the atmosphere quicker, our measurements indicate there cannot be much methane being put into the atmosphere by any mechanism, whether biology, geology, or by ultraviolet degradation of organics delivered by the fall of meteorites or interplanetary dust particles," Atreya added.

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